The Concrete Industry’s Weakest Link?

This article sheds light on the knowledge and communications gap that exists between structural engineers and concrete materials engineers, and why changes are essential if the concrete industry is to move forward via improved durability and constructability.

The information addressed here may be considered by some structural engineers as controversial in nature, while other engineers may consider it downright sacrilegious; however, this article was not written for the great many structural engineers and design professionals that already understand the important roles that durability and constructability play in achieving success, but for those great many that still do not. Many design structural engineers today still focus an overabundance of attention on the mechanical properties of concrete, paying minimal or no attention to the durability and constructability aspects of the design, and as a result, economics and long-term serviceability often suffers.

Being a structural engineer by education and a concrete materials engineer with over 30 years of experience, without reservation, it is a fact, not just a belief that light must be shed upon this knowledge and communications gap hindering advancements if the industry is to construct future concrete structures more economically and having greater longevity with a reduced need for major repairs throughout the design life of the structure.

As the saying goes, a chain is only as strong as its weakest link. In the concrete industry, one of the weakest, if not the weakest link that exists is the clear and present knowledge and communications gap between the disciplines of structural engineering and concrete materials engineering.

For a successful concrete structure, three fundamental properties should be considered from the inception of the design process: (1) mechanical properties, (2) durability properties, and (3) constructability. Failure to consider all three can set the stage for a multitude of problems, both during and after construction. Neglecting to consider all of these three fundamental properties can sacrifice both economy and long-term serviceability. In the case of concrete structures exposed to harsh conditions,?durability, not mechanics frequently governs the design.

In the past few decades, the concrete industry has been making strides focusing greater attention on the importance of durability, but as an industry, we still have a long way to go. Again, in spite of the fact that there are already many astute design professionals that intimately understand the important roles that durability and constructability properties play in the design of a successful concrete structure, a surprising number still do not. Many design professionals still focus a disproportionate amount of attention on concrete's mechanical properties, most often compressive strength, with the false belief that if the measured compressive strength of test specimens is satisfactory, the structure will perform well throughout its life. However, nothing can be farther from the truth! Why??Because the overwhelming majority of failures that occur with concrete structures are not due to mechanical deficiencies, but rather are traceable to one or more forms of a durability-related failure, which can ultimately lead to mechanical deficiencies and unsafe conditions.

Structural design codes for new construction, such as ACI 318, contain provisions addressing durability. Durability-related properties in ACI 318 that need to be considered by the licensed design professional include: (1) concrete exposed to cyclic freezing and thawing in the presence of moisture with or without deicing chemicals, (2) concrete in contact with soil or water containing deleterious amounts of water-soluble sulfates, (3) concrete in contact with water requiring low permeability, and (4) concrete requiring corrosion protection of embedded bars and strands. When warranted, other important durability-related properties that should be considered include, but are not limited to, concrete subject to chemical attack and abrasion.

With respect to constructability, what looks good on paper might in actuality be difficult or even impossible to build. This has been demonstrated through a multitude of case histories. For example, excessively close spacing of reinforcing bars can result in extremely challenging placement conditions unless costlier concrete mixtures that were not originally specified are used, such as flowing concrete or self-consolidating concrete. Insomuch as constructability is commonly viewed as a contractor's responsibility, design professionals should always keep constructability in mind from design inception. It may look good on paper, but can it be built? And if so, is it reflected in the plan notes and specifications and available for pre-bid review by the contractor?

Other than the above-stated example, improvements to concrete constructability is beyond the scope of this article; however, improvements made to the constructability of a concrete structure would include: (1) improved project productivity, (2) improved scheduling, and (3) lower overall project cost.

Generally speaking, structural engineers speak one language whereas concrete materials engineers speak an entirely different language. The laws governing durability are significantly different, and in many cases vastly more complex than those governing mechanics. In order to advance towards creating more durable and constructable concrete structures, this communications barrier that is hindering industry advancement must be overcome; therefore, more collaboration is needed between structural engineers and concrete materials engineers throughout the design process.

Closing the gap between these two disciplines is long overdue if we are to advance in producing concrete structures having better longevity with substantially reduced needs for major repairs, while still satisfying the mechanical properties necessary for code compliance and public safety.?